Automated door assembly, press, and adhesive therefor

ABSTRACT

Provided is a system and method of making a door having first and second door skins and an internal frame. The top and bottom surfaces of the frame are coated with an adhesive and the frame is placed on a first door skin. The second door skin is then placed on the opposite surface of the frame. The assembled components are then pressed to bond the first and second door skins to the frame.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIMS TO PRIORITY

This application is related to Provisional Application No. 61/368,604,filed Jul. 28, 2010, and Provisional Application No. 61/368,889, filedJul. 29, 2010 the disclosures of which are incorporated herein byreference and to which priority is claimed.

FIELD OF THE INVENTION

The present invention is directed to an automated system and method formanufacturing a door having first and second door facings and aninternal door frame.

BACKGROUND

Doors are typically made from two molded or flush door skins attached toopposite sides a central door frame. The door facings are often moldedfrom a wood fiber and resin compound, although fiberglass resin formedpolymer door facings are known. The door frame typically includes stilesand rails made of wood located around the perimeter of the door. Theinterior of the door may optionally include a core.

Manual assembly of doors is relatively labor intensive, expensive, andsubject to quality variations. During manual assembly, a door facing isplaced on a production table with its intended exterior surface facedown. Adhesive is then applied to the stiles and rails of a frame. Theadhesively coated frame parts are then placed on the door facing on thetable. Adhesive applied to a second side of the stiles and rails facesupwardly and a second door facing is placed with its exterior surfaceface upon the second side of the frame. The resulting assembled door isstacked at a holding station so that additional doors may be assembled.The assembled doors should be handled carefully, given that thecomponents of the door can easily shift during transportation.

Each successive door assembly is stacked on top of the previous doorassembly until a predetermined quantity of door assemblies has beenstacked. The stack of door assemblies is then transported to and loadedin a press. The press applies pressure to the entire stack for a periodof time sufficient to allow the adhesive to bond the door facings to theframe. Conventional adhesives, such as polyvinyl acetate, may takeapproximately thirty minutes or more in-press before the door reaches“green” strength. The door achieves green strength when the adhesive hasreached sufficient bonding strength to hold the door components togetherfor further handling.

Once an acceptable green strength is achieved, the doors may be removedfrom the press and moved to an in-process inventory until the adhesivereaches maximum cure strength. Depending on the adhesive used, the doorsmay need to remain in inventory for a relatively long period of time,for example two hours or more, or even as long as twenty-four hours,before the adhesive reaches maximum bonding strength.

After reaching maximum cure strength the doors are then moved to a finalprocessing station. Final processing includes edge trimming the doors tocustomer specification and optional coating and/or painting of doorskins and exposed edges of the stiles and rails around each doorperimeter. Using this process, manufacturing time for a door may betwenty-four hours or more, from the time production is initiated to theresulting finished door is complete.

SUMMARY

In accordance with an embodiment, a door-making system includes at leastone coating station, at least one assembly station, and at least onepressing station. The coating station applies adhesive to at least oneof a door frame, a first door skin, and a second door skin. The assemblystation joins the first and second door skins to opposite surfaces ofthe frame. The pressing station includes a first press and a secondpress for alternately receiving the assembled doors.

In accordance with a further embodiment, a door pressing stationincludes at least one press having an upper die and a lower die. Theupper die has an upper convex surface and the lower die has a lowerconvex surface. The upper and lower convex surfaces face one another todefine a mold cavity.

In accordance with a further embodiment, a method of making a doorincludes adhesively bonding a first door skin and a second door skin toopposite sides of a frame to assembly doors as part of a productionprocess. The assembled doors are alternately received in a first pressand a second press.

In accordance with another embodiment, a method of pressing an assembleddoor includes loading an assembled door into a press having an upper diewith an upper convex portion and a lower die with a lower convexportion. The upper and lower convex surfaces face one another to pressthe door assembly.

Other embodiments, including apparatus, systems, methods, and the likewhich constitute part of the invention, will become more apparent uponreading the following detailed description of the exemplary embodimentsand viewing the drawings. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory only and therefore not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary automated door productionline.

FIG. 2 is a sectional, plan view of a defective door.

FIG. 3A is a plan view of an exemplary door facing having adhesiveapplied thereto.

FIG. 3B is a plan view of another exemplary door facing having adhesiveapplied thereto.

FIG. 4 is a plan, schematic view of an exemplary double press.

FIGS. 5A-5C are sectional, schematic views of an exemplary pressingprocess for a door assembly.

FIG. 6 is a sectional, schematic view of an exemplary press and doorassembly.

FIG. 7A is a plan view of an exemplary post-press door assembly.

FIG. 7B is a sectional, plan view of the door assembly of FIG. 7A takenalong line 7B-7B.

FIG. 7C is a sectional, plan view of the door assembly of FIG. 7A takenalong line 7C-7C.

FIG. 8 is a sectional, schematic view of a door assembly in an exemplarydoor press utilizing spacers.

FIG. 9 is a sectional, schematic view of a door assembly in an exemplarydoor press utilizing attached plates.

FIG. 10 is a sectional, schematic view of a door assembly in anexemplary door press utilizing membranes.

FIG. 11 is a sectional, schematic view of a door assembly in anexemplary door press utilizing expandable membranes.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S) AND EXEMPLARY METHOD(S)

Reference will now be made in detail to exemplary embodiments andmethods as illustrated in the accompanying drawings, in which likereference characters designate like or corresponding parts throughoutthe drawings. It should be noted, however, that the invention in itsbroader aspects is not limited to the specific details, representativedevices and methods, and illustrative examples shown and described inconnection with the exemplary embodiments and methods.

FIG. 1 depicts an automated door production line 1. In an exemplaryembodiment, the door production line 1 is a synchronous system designedto operate at a specific rate of movement, for example, one doorproduced per unit of time. In order to avoid bottlenecks, each step inthe process, including transportation, occurs at the specific rate ofmovement. Therefore, it is important to provide suitable press time andproper adhesive application to sufficiently bond the components of thedoor together. Improper bonding can lead to quality issues.

FIG. 2 shows a door D1 having such quality issues. Improper bonding timecan cause the separation or delamination of the door skins S1, S2 fromthe core element C. Delamination is especially persistent in door skinsS1, S2 having a number of molded panels. For example, molded six paneldoor skins S1, S2 bonded to a core C with a hot melt adhesive usingconventional processes may experience delamination across the width ofthe door D1. The delamination between skins S1, S2 and the core C is anindication of internal polyurethane (PUR) adhesive bond failure whichmay be caused by tension stresses or spring-back of the bowed skins andcompressed core areas in the ovolos, or molded panel design areas, ofthe molded skins S1, S2. In these cases, the initial green or setstrength of various PUR formulations along with typical PUR roll coatingand door pressing approaches may not overcome the stresses leading todelamination. Pre-cured back surfaces of the door skins S1, S2 may alsoprevent effective PUR wetting when the adhesive is applied only to theframe. To overcome these deficiencies various improvements in theprocess have been made.

FIG. 1 shows the production line 1 having an exemplary series ofstations for assembling a door. Various material handling and movementdevices and methods may be used to transport components of the doorassembly, and are simply designated by the arrows in the individualstations and between stations. Material handling and movement devicesmay include, for example, conveyors, gantry, manipulators, grippers,automated guided vehicles, and automated storage/retrieval systems. Thecomponents and stations of the production line may be operated by anoperator's control, automatically utilizing various sensors includingoptical, magnetic, and radio sensors, or any combinations of manual andautomatic operation. Though specific examples of material handling andmovement may be provided in the exemplary description of certainstations, these may be modified as would be understood by one ofordinary skill in the art upon viewing this disclosure.

As shown in FIG. 1, a stile assembly station 10 includes a lock blockindexing device 12 and a stile indexing device 14. In an exemplaryembodiment the stile indexing device 14 removes stiles 2 from a firststile conveyor 16 and a second stile conveyor 18. A single stileconveyor, a set of first and second stile conveyors 16, 18, or more thantwo stile conveyors may be utilized depending on the throughput rate.More stile conveyors or sets of stile conveyors allow an increase in thethroughput rate of the production line 1. When a pair of stiles 2 havebeen removed from the top level conveyor of the first and second sets ofstile conveyors 16, 18, a new pair of stiles 2 is delivered to the toplevel conveyor to replace them. Because conveying the stiles 2 to theappropriate position to be picked up by the stile indexing device 14 maytake longer than the movement rate of the system, the stile indexingdevice 14 alternatively may take the next pair of stiles 2 from the nextlevel of conveyors.

As the stiles 2 are being retrieved by the stile indexing device 14,lock blocks 4 are removed by the lock block indexing device 12 and movedalong a conveyor 20 or other suitable material transportation device.The lock blocks 4 may be removed by the lock block indexing device 12 ina manner similar to the stiles 2, or the lock blocks 4 may be removedfrom a pallet containing multiple lock blocks 4. Both the stiles 2 andthe lock blocks 4 are moved to a lock block attachment station 22. Atthe lock block attachment station 22, the lock blocks 4 are connected tothe stiles 2. The lock blocks 4 may be attached to the stiles 2 viaadhesive, for example a hot melt adhesive, a mechanical fastener, or acombination thereof. While FIG. 1 depicts a lock block 4 being attachedto each stile 2, optionally only a single lock block 4 may be attached.The movement and handling of all the components in stations 10 and 22may be handled manually or automatically by robotic systems such as pickand place robotic arms, robotic indexers, and the like.

Rail assembly station 24 includes a rail indexing device 26 whichselects a pair of rails 6 a, 6 b from a rail conveyor system 28. In anexemplary embodiment the rail conveyor system 28 includes a top railconveyor 30 and a bottom rail conveyor 32, though a single railconveyor, or more than two rail conveyors may alternatively be used asdiscussed above in connection with the first and second stile conveyors16, 18. As shown in FIG. 1, a single top rail 6 a may be selected fromthe top rail conveyor 30 and a single bottom rail 6 b is selected fromthe bottom rail conveyor 32. In various exemplary embodiments, a doorhaving more than one top rail 6 a, such as a double top rail (notshown), more than one bottom rail 6 b, such as a double bottom rail (notshown), or both a double bottom rail and double top rail, and/or one ormore intermediate rails (not shown) may be desired. Therefore, the railindexing device 26 may be capable of variably selecting a single rail 6a, 6 b or multiple rails from the top rail conveyors 30, the bottom railconveyors 32, and optionally intermediate rail conveyors (not shown). Ifmore than a single top and/or bottom rail 6 a, 6 b is selected, the tworails 6 a, 6 b are attached, for example, by fasteners or an adhesivesuch as a hot melt adhesive to form the double rail.

After being selected, the rails 6 a, 6 b are moved to a core attachmentstation 34. At the core attachment station 34, a core C is connected tothe top rail 6 a and the bottom rail 6 b, for example, by a hot meltadhesive. The core C may be brought to the core attachment station 34 bya conveyor or indexing device (not shown) similar to those shown anddescribed with respect to the lock blocks 4, stiles 2, or rails 6 a, 6b. The core C may be an expandable core or a solid core, such as,fiberboard, or any suitable substance depending on the door. In anexemplary embodiment, the core C is an expandable corrugated cardboardcore or honeycomb paper core. The production line 1 may be set up andutilized so that the core C is variable and optional so that differentcores C may be selectively attached to the rails or omitted from theassembled frame. Optionally the core may be formed in situ.

The attached lock block 4 and stile 2 assembly and the attached rail 6a, 6 b and optional core C are then transferred to the frame assemblystation 36. Robotic handling devices such as a clamp and gantry systemmay be used to deliver the frame components to the frame assemblystation 36. When an expandable core C is used, the rails 6 a, 6 b may bedrawn apart to expand the core C. The rails 6 a, 6 b and stiles 2 arethen attached together to form an assembled frame F. The rails 6 a, 6 band stiles 2 may be attached with mechanical fasteners, an adhesive, forexample, a hot melt adhesive, or any combination of fasteners andadhesive. In various exemplary embodiments, different combinations ofthe lock blocks 4, stiles 2, rails 6 a, 6 b, and core C may bepreassembled before reaching the production line. It should be notedthat the term frame F used throughout the rest of this descriptionincludes the assembled stiles 2, rails 6 a. 6 b, optional lock block(s)4, and optional core C.

When the frame F is assembled, either through the assembly system andprocess described above, preassembly, or a combination thereof, theframe F is moved to a frame adhesive station 38. In an exemplaryembodiment, the frame adhesive station 38 is capable of applying anadhesive to both sides of the frame F. Adhesive application may beaccomplished by passing the frame F through a double roll coater of theframe adhesive station 38. In an exemplary embodiment, the roll coaterapplies adhesive to the frame F in an amount between about 6 and about35 g/sft (grams per square foot) as measured on a surface of the stiles2 or rails 6 a, 6 b. In various exemplary embodiments, the amount ofadhesive is between about 15 and about 26 g/sft. This amount of adhesivemay help prevent quality issues, such as pillowing discussed above.After the adhesive is applied, the frame F is transferred to a door skinassembly station 40. Robotic handling devices such as a clamp and gantrysystem 39 may be used to deliver the frame from the frame adhesivestation 38 to the door skin assembly station 40.

The door skin assembly station 40 includes a first skin feeder 42 and asecond skin feeder 44. The first skin feeder 42 may include a door skinpallet 46 a or multiple pallets of door skins. Similarly, the secondskin feeder 44 may include a door skin pallet 46 b or multiple palletsof door skins S1, S2. In an exemplary embodiment, the first skin feeder42 provides a bottom door skin S2 and the second skin feeder 44 providesa top door skin S1. The top and bottom door skins S1, S2 may beidentical or different depending on the production requirements. The topand bottom door skins S1, S2 may be any variety of door skins includingwood composite door skins, solid wood door skins, polymer door skins,sheet molding compound door skins, molded door skins, and flush doorskins. Though two skin feeders 42, 44 are shown, a single skin feedermay be utilized which provides both the top and bottom door skins S1,S2.

Door skins S1, S2 may be unloaded from the pallets 46 a, 46 b and placedon a conveyor (not shown) either manually or through a robotic handlingdevice such as a vacuum gantry. If the door skins S1, S2 are removedfrom the pallets 46 a, 46 b manually, the operator moving the door skinsS1, S2 may perform a visual quality inspection. If a door skin S1, S2 isfound to be unsatisfactory, the operator may place it on a disposalconveyor. If the door skin S1, S2 is found to be acceptable, theoperator may place it on a production conveyor. Alternatively, the doorskin S1, S2 may be removed from the pallets 46 a, 46 b with an automateddevice and a camera or set of cameras may be set up so that a remoteoperator can perform visual inspection. The operator is then able todetermine if the door skins S1, S2 are acceptable and signal the robotichandling system to place the door skins S1, S2 on either the productionconveyor or the disposal conveyor. In various exemplary embodiments, theinspection may be performed automatically by tactile inspection devices,such as touch probes, or non-tactile inspection devices, such as laseror optical sensors. For example, a camera may optically capture theimage of a door skin S1, S2. The image may then be processed andmeasured by a microprocessor. If the door skin S1, S2 is acceptable, themicroprocessor can signal the robotic handling device to place the doorskin S1, S2 on the production conveyor. If the door skin S1, S2 is notaccepted, the microprocessor signals the robotic handling device toplace the door skin S1, S2 on the disposal conveyor.

The first and second pallets 46 a, 46 b may have door skins S1, S2facing the same direction. For example, the door skins S1, S2 in pallets46 a, 46 b may have an intended exterior surface (depicted in white)facing up. Depending on the parameters of the production line 1, thedoor skins S1, S2 from one or both pallets 46 a, 46 b may need to beflipped so that their intended interiorly disposed surface (shaded) isfacing down. In the exemplary embodiment shown in FIG. 1, after a doorskin S2 is removed from the first skin feeder 42, it is transferred to afirst flipping station 48. The first flipping station may utilize anyautomated flipping apparatus, for example a star conveyor. Optionally,before the bottom door skin S2 is connected to the frame, a firstadhesive applicator 50 applies a layer of adhesive to the interiorsurface of the door skin S2. The first adhesive applicator 50 may be afirst spray coater with one or more spray heads.

In various exemplary embodiments, the first adhesive applicator 50 iscapable of applying adhesive to the door skin S2 in beads or lines. Asbest shown in FIGS. 3A and 3B, the device may be a nozzle or jet capableof applying under pressure a liquid form of an adhesive, for example ahot melt adhesive such as PUR or ethylene vinyl acetate (EVA), to a doorskin S2. The adhesive may be applied in individual lines, such as thewavy lines Al as shown in FIG. 3A. The adhesive lines Al are verticallyorientated and placed just outside of and down the middle of the panelsP. The type of adhesive application shown in FIG. 3A is one way toprevent delamination of the door skin S2 from the core C.

In the exemplary embodiment shown in FIG. 3B, a bead A2 of adhesive isapplied to each panel P. Applying the adhesive to the door skin S2 inthis way creates a spot-weld-type gluing effect when the door skin S2 ispressed to the core C, further bonding the door skin S2 and the core Creducing the chance of delamination. Various other glue patterns, suchas a web pattern or a checkered pattern, or combinations of gluepatterns may be utilized depending on the configuration and design ofthe door skins S1, S2. In various exemplary embodiments, the firstadhesive applicator 50 is capable of applying different adhesives in avariety of patterns and locations so that different door types may bemade on a single production line 1. adhesively coated frame F istransported to the first door assembly station 52 and placed onto thebottom door skin S2. Various stops, limits, tactile sensors, andnon-tactile sensors may be used to align and position the bottom doorskin S2 and the frame F.

Similar to the bottom door skin S2, the top door skin S1 is transferredfrom the second skin feeder 44. The top door skin S1 may have anoptional adhesive coating applied by a second adhesive applicator 54.The second adhesive applicator 54 may include all the features andcapabilities discussed above with respect to the first adhesiveapplicator 50. Accordingly, the second adhesive applicator 54 may beidentical to or different from the first adhesive applicator 50.

As discussed above, the second pallet of skins 46 b has the exteriorsurface of the top door skins S1 facing up. Therefore, to apply adhesiveto the interior surface, the top door skin S1 is flipped at a secondflipping station 56. Because the top door skin S1 is placed onto the topsurface of the frame F, it must be flipped again at a third flippingstation 58 after the adhesive is applied. Various exemplary embodimentsmay omit application of adhesive to the top door skin S1 and thereforethe second and third flipping stations 56, 58 may be bypassed oromitted. Additionally, the second adhesive applicator 54 may be capableof applying adhesive from underneath the top door skin S1 so that thesecond and third flipping stations 56, 58 may be omitted. Alternatively,the door skins S1, S2 in pallets 46 a, 46 b may be providedinterior-side up so as to avoid the use of the flipping stations 48, 56.

After the optional adhesive application, the top door skin S1 is movedto a second door assembly station 60. At the second door assemblystation 60 the top door skin S1 is placed onto the frame F opposite thebottom door skin S2 so that the interior surface of the top door skin S1faces down towards the frame F. Various stops, limits, tactile sensors,and non-tactile sensors may be used to align and position the door skinS1 and the frame F.

In various exemplary embodiments, the door skin assembly station 40includes a device or devices for applying a liquid, for example water,to the inner surface of the door skins S1, S2 before they are attachedto the frame. A spray head or other suitable device can apply water, forexample in a misting spray, to the inner surface of the door skins S1,S2. The liquid may be applied by the first and second adhesiveapplicators 50, 54 in connection with an adhesive or variably without anadhesive. Alternatively, the liquid may be applied prior to, orsubsequent the optional adhesive application. The application of waterhelps prevent warping and may improve skin wetting and increase the bondquality between resin that may be present in the door skins S1, S2 andthe frame and the core C. The amount of water applied is enough todampen the inner surface of the door skins S1, S2, though more water maybe applied so that the moisture permeates at least partially into thedoor skins S1, S2. Other surface treatments may also be applied to thesurface in addition to water or alternatively to water in order toincrease bond quality.

After the top door skin S1 is connected to the frame F, the assembleddoor is transferred to a pressing station 61 where the door is pressedto more fixedly bond the door skins S1, S2 to the frame F and core C. Asdiscussed above, because the production line 1 is automated, each stepis performed at the set rate of movement to avoid bottlenecks. Forexample, the amount of time for the lock block attachment station 22 toattach the lock blocks 4 to the stiles 2 is equal to rate of movement,the time for the frame F to be transferred to the first door assemblystation 52 equals the rate of movement, and the time in betweencompleted doors coming off the production line 1 is equal to the rate ofmovement. In various exemplary embodiments, the rate of movement of thepresently described system is about 7 seconds to about 15 seconds, forexample about every 8 seconds, though the time may vary depending onseveral factors such as the adhesive selected, as would be understood byone of ordinary skill in the art upon viewing this disclosure. The rateof movement may not be long enough, however, for sufficient bondstrength to form between the door skins S1, S2 and the frame F and coreC.

To allow for a pressing time that exceeds the rate of movement, a doublepress 62 is used. The double press includes an upper press 62 a and alower press 62 b. As shown in FIG. 1, a first assembled door istransferred onto a loading table 63 a. The loading table 63 a may be atwo-position table and may include a conveyor device, such as poweredrollers, to move the assembled doors on and off the loading table 63 a.The loading table 63 a places an assembled door into one of the top andbottom presses 62 a, 62 b, for example the bottom press 62 b. After theproduction line 1 moves again, a second assembled door is loaded ontothe loading table 63 a and the loading table 63 a is raised to place thesecond assembled door into the upper press 62 a. After the productionline 1 moves again, the first assembled door is removed from the lowerpress 62 b and transferred to a discharging table 63 b. The dischargingtable 63 b may be a two-position table and may include a conveyordevice, such as powered rollers, to move the assembled doors on to andoff of the discharging table 63 b. As the first door is transferred fromthe lower press 62 b, the loading table 63 a places a third assembleddoor in the lower press 62 b to replace the first assembled door. Usingthe double press 62, the pressing of assembled doors is alternatedbetween the upper and lower presses 62 a, 62 b. An assembled door cantherefore undergo a pressing operation, which may include the openingand closing the dies of the upper and lower presses 62 a, 62 b, forapproximately twice as long as the rate of movement. The extra presstime allows a greater bond to be created between the door skins S1, S2,and the frame F and the core C.

In various exemplary embodiments, the press imparts approximately 100psi to the door skins S1, S2 adjacent the stile and rail sections. Thepressure along the remaining areas of the door skins S1, S2 covering thecore C varies.

The double press 64 may also be capable of rapid closure. For example,an upper die 70 and a lower die 74 in each of the upper and lowerpresses 62 a, 62 b of the double press 62 may be capable oftransitioning from an open position to contacting the door skins S1, S2and reaching a final pressure in less than 10 seconds. In variousexemplary embodiments, the double press 62 is capable of reaching finalpressure in approximately one second or less. A fast closing doublepress 62 allows for a faster acting adhesive to be used and thereforequicker set and cure times.

In various exemplary embodiments, one of the upper and lower dies 70, 74or both dies 70, 74 may be moved towards and away from the assembleddoor to close the press. As best shown in FIG. 4, actuators 64, such ashydraulic or pneumatic cylinders may be connected to the upper die 70.FIG. 4 depicts the upper press 62 a in an open position and the lowerpress 62 b in a closed position. Each upper and lower press 62 a, 62 bmay also include a conveyor 65, for example a belt conveyor or poweredrollers, to assists in loading and discharging the assembled door fromthe respective press 62 a, 62 b. In an exemplary embodiment, at leastpart of the conveyor 65 is arranged to position the bottom door skin S2above a stationary lower die 74. As best shown in FIG. 4, the lower die74 may be located between the top part of the conveyor 65 and thebottom, or return, part of the conveyor 65. During the pressingoperation, the upper die 70 closes, pressing the door assembly againstthe conveyor 65 and the lower die 74. The conveyor 65 should be madefrom a flexible material that is durable enough to withstand thepressure applied by the dies 70, 74. In various exemplary embodiments,the conveyor 65 may include a first side and a second side with an opencenter section (not shown). The first and second side may include beltsor rollers and be positioned along the edges of the door to contact thedoor skins S1, S2 adjacent the frame F. The first and second sideconveyors and open center section allow the lower die 74 to contact thecentral region of the bottom door skin S2 directly. Various otherdevices and methods for positioning the assembled doors D2 into theupper and lower presses 62 a, 62 b, for example a push rod, may also beused. The press 62 may also include various stops, limits, tactilesensors, and non-tactile sensors may be used to align and position thedoor to square the frame F before pressing.

Although the exemplary embodiments discussed above are with respect to adouble press 62, it should be understood that the pressing apparatus mayalternatively have three, four, five, or more presses. As the number ofpresses increases, the pressing time per press can likewise increasewithout slowing the overall movement time. Moreover, the presses 62 a,62 b may be placed side-by-side on the same level or otherwise orientedas opposed to the stacked relationship shown in FIG. 1. Various materialhandling devices, such as a switching conveyor, may provide theassembled doors to the presses 65 a, 65 b in an alternating fashion.

As shown in FIGS. 5A-5C, in various exemplary embodiments both the upperand lower presses 62 a, 62 b of the double press 62 include an upper die70 having a convex portion 72 a and a lower die 74 having a convexportion 72 b. The convex portions 72 a, 72 b over compress at least thecentral portions of the top and bottom door skins S1, S2 so that atleast part of the interior surface of the door skins S1, S2 is coplanarwith or below the respective surface of the frame F to which the skin isattached. The over compression helps increase the bond between the doorskins S1, S2 and the core C. In various exemplary embodiments, theradius of curvature of the convex portions 72 a, 72 b is between about0.1 mm and about 2 mm. In certain embodiments the radius of curvature ofthe convex portions 72 a, 72 b is between about 0.2 mm and approximately0.5 mm. The radius of curvature of the convex portions 72 a, 72 b mayvary however, depending on design and production characteristics such asthe design of the door, the size of the door, the press time, and theamount of pressure applied.

FIGS. 5A-5C depict an exemplary embodiment where the convex portions 72a, 72 b begin approximately at the outer edges of the upper and lowerdies 70, 74. In an exemplary embodiment shown in FIG. 6, a flat section75 a. 75 b extends around the outer edge of the dies 70, 74, and theconvex portions 72 a, 72 b begin in a more centrally located region. Theflat sections 75 a, 75 b may have approximately the width of typicalstiles on the longitudinal sides and the width of typical rails on thelateral sides. The flat section 75 a, 75 b may also be slightly largerthan a standard frame F size to accommodate different width doors, asthe size of the convex sections 72 a, 72 b may be varied and stillobtain desirable results. For example, relatively small central convexsections 72 a, 72 b compared to the length and width of a standard doormay be provided in the upper and lower dies 70, 74 which could stilleffectively reverse the natural bowing of the door skins S1, S2 andtherefore help prevent pillowing and delamination.

As best shown in FIG. 5A, when the door is placed into the press astrong adhesive connection may be present between the perimeters of thedoor skins S1, S2 and the stiles 2 and rails 6, but internal stresses inthe door skins S1, S2 may lead to pillowing and separation from the coreC. The pillowing effect can cause separation between the door skins S1,S2 and the core C of as much as 1 inch or greater, and can reach about 2inches at the very center of the door skins S1, S2. As shown in FIG. 5B,when the press is closed, the convex portions 72 a, 72 b over compressthe central portion of the door skins S1, S2 respectively. The overcompression not only helps to bond the door skins S1, S2 to the core C,but also redirects the natural bowing of the door skins S1, S2. Becausethe door skins S1, S2 are fixed at the frame F, the internal forces havea tendency to push away from the frame F, forcing the door skins S1, S2away from the core C. Once the bowing is reversed, any internal stressesremaining in the door skins S1, S2 are redirected inwards, pushing thecenter of the door skins S1, S2 towards the core C as opposed to awayfrom it. As shown in FIG. 5C, when the press 64 is opened, the pillowingis eliminated and the door skins S1, S2 may return to an approximatelyflat shape. The resultant door has increased bond strength compared totypical doors with less chance of pillowing or delamination.

In various exemplary embodiments, the door skins S1, S2 may have aslight concave cross-sectional shape after pressing is complete. FIG. 7Ashows a pressed door D2 and FIGS. 7B and 7C depict cross-sectional viewsof FIG. 7A showing the concave shape imparted to the door D2. It shouldbe noted that the concave sectional profile shown in FIGS. 7B and 7C maynot be to scale. The concave shape retained in the door skins S1, S2after pressing is completed is due to the fact that the door skins S1,S2 may undergo plastic deformation resulting from the over compressionand therefore will not return to a planar surface after the pressingoperation. The concave shape, however, may be less than noticeable bythe unaided human eye and therefore undetectable to consumers. Forexample, the resulting shape of the door skins S1, S2 may have a maximumconcave depth that is less than the maximum convex height of the upperand lower dies 70, 74. In various exemplary embodiments, the maximumdepth of the concave section, when present, is about 0.05 mm to about0.5 mm.

FIGS. 5A-5C depict an exemplary embodiment where the convex portions 72a, 72 b are formed integrally with the upper and lower dies 70, 74. Invarious other exemplary embodiments an upper spacer 76 a and a lowerspacer 76 b are inserted between the upper and lower dies 70, 74 and thedoor skins S1, S2 respectively as shown in FIG. 8. The spacers 76 a, 76b may be made from a rigid material, for example a metallic material, orthey may be made from a resilient material such as a silicone, polymer,elastomer, wood, or cardboard. The spacers 76 a, 76 b may have a convexshape similar to the dies 70, 74 shown in FIGS. 5A-5C, or they maysimply provide a raised area to over compress the door skins S1, S2. Theuse of spacers 76 a, 76 b allows different sizes, shapes, and amounts ofcontour to be interchanged for different door sizes and designs. A humanoperator or robotic handling device may place the spacers 76 a, 76 bbetween the door skins S1, S2 and the upper and lower dies 70, 74 as theassembled door is loaded into the double press 64. The spacers 76 a, 76b may also be placed either above or below the top belt of the conveyor65 when used in conjunction with the exemplary embodiment depicted inFIG. 4. The handling device may determine the type of spacers 76 a, 76 bappropriate for the door based on information received from an operator,a central computing system, through image recognition, or various othertechniques associated with variable batch production.

In various other exemplary embodiments, the convex or raised portion isachieved through an upper plate 78 a and a lower plate 78 b that areattached to the upper and lower dies 70, 74 as shown in FIG. 9. Theupper and lower plates 78 a, 78 b may be made from various materialsincluding elastomeric, metallic, ceramic, cellulosic, or compositematerials. Multiple upper and lower plates 78 a, 78 b may be used, eachhaving a different size, shape, and/or radius of curvature. Thedifferent upper and lower plates 78 a, 78 b may be used in associationwith different door sizes and designs. The upper and lower plates 78 a,78 b may be removably connected to the upper and lower dies 70, 74. Forexample, the plates 78 a, 78 b may be attached to the upper and lowerdies 70, 74 through removable mechanical fasteners such as bolts orlatches, or through a magnetic connection. Different upper and lowerplates 78 a, 78 b may be interchanged manually or automatically asdiscussed above in relation to the upper and lower spacers 76 a, 76 b.

In various exemplary embodiments, the over compression of the door skinsS1, S2 is achieved through an upper membrane 80 a and a lower membrane80 b fastened to the upper and lower dies 70, 74 as shown in FIG. 10.The membranes 80 a. 80 b may have a thickness of about 0.1 mm to about2.0 mm. The membrane may be made from a material that allowsdifferential compression, such as a material comprising silicone orrubber. When pressed onto the door skins S1, S2, the compression of theupper and lower membranes 80 a, 80 b is greatest at the areas adjacentthe rails and stiles 82 and decreases towards the center of the door 84.Therefore the upper and lower membranes 80 a, 80 b are thicker at thecenter of the door skins S1, S2 and cause over compression. The variablecompression allows a single set of upper and lower membranes 80 a, 80 bto press different door sizes and designs. Accordingly, the upper andlower membranes 80 a, 80 b may be permanently attached to the upper andlower dies 70, 74 or they may be semi-permanently attached where asecure constant connection is desired but replacement upper and lowermembranes may be provided. In various embodiments, however, the upperand lower membranes 80 a, 80 b may be removably secured to the upper andlower dies 70, 74 so that membranes 80 a, 80 b of different sizes,shapes, materials, or any combination thereof may be easilyinterchanged.

In various exemplary embodiments, the convex or raised portion isachieved through an upper expandable membrane 86 a and a lowerexpandable membrane 86 b attached to the upper and lower dies 70, 74 asshown in FIG. 11. The expandable membranes 86 a, 86 b are made of anexpandable or otherwise flexible material. Gas, such as compressed air,is supplied to upper and lower chambers 88 a, 88 b formed between theupper and lower dies 70, 74 and the upper and lower expandable membranes86 a, 86 b respectively. The added pressure from the gas is transferredto the door skins S1, S2 and causes over compression during pressing.Though only a single chamber 88 a, 88 b is shown in FIG. 11 associatedwith each die 70, 74, there may be more than one chamber and thechambers may be selectively supplied with gas to provide differentamounts of compression to different door sections or to different doorsizes and designs.

As best shown in FIG. 1, after the pressing station 62, the assembleddoor D2 is taken off the main production line 1. The door D2 then maypass through a number of optional finishing operations as needed. Forexample, the door may be passed through a stile trimming station 90 anda rail trimming station 92 to remove excess material. If the blades ofthe trimming stations 90, 92 are parallel the door may need to berotated between the stile trimming station 90 and the rail trimmingstation 92. After the edges have been trimmed, the door may be placedthrough an edge coating station 94. Here the edges of the door, such asthe exposed rails 6 a, 6 b and stiles 2 are coated or painted. Otherpainting or coating may be accomplished at this station or separately.

When the door D2 is completed, it passes to an inspector 96 who checksthe door for quality issues. In various exemplary embodiments thequality inspection may be performed automatically as discussed abovewith respect to the door skin assembly station 40. Any unacceptable dooris either discarded or reworked, and all doors passing inspection aresent to palletizer 98 for stacking.

A number of commonly used and commercially available adhesives have beendiscussed above such as PUR and EVA hot melt adhesives. However, aspectsof the present invention are also directed to the novel use of adhesivecompositions. In an exemplary embodiment, a PUR adhesive comprisingpolyurethane and isocyanurate is used in the above-disclosed system. Ina separate embodiment, an adhesive comprising polyurethane andcyanoacrylate is used in the above-identified system. These chemicalsincrease the initial green or set strength of the adhesives, securingthe bond between the door skin and the frame, eliminating delaminationcaused by the stresses of bowed or warped skins.

The foregoing detailed description of the certain exemplary embodimentshas been provided for the purpose of explaining the principles of theinvention and its practical application, thereby enabling others skilledin the art to understand the invention for various embodiments and withvarious modifications as are suited to the particular use contemplated.This description is not necessarily intended to be exhaustive or tolimit the invention to the precise embodiments disclosed. Additionalembodiments are possible and are intended to be encompassed within thisspecification and the scope of the appended claims. The specificationdescribes specific examples to accomplish a more general goal that maybe accomplished in another way.

What is claimed is:
 1. A door-making system, comprising: at least onespray coating station for spraying adhesive to a door frame havingstiles and rails forming a perimeter of the door frame, a first doorskin, or a second door skin; at least one assembly station for joiningthe first and second door skins to opposite first and second surfaces ofthe door frame, respectively, to form assembled doors; a pressingstation for alternatingly pressing at least two of the assembled doors,the pressing station comprising at least a first press and a secondpress vertically stacked one on top of another for receiving at leasttwo of said assembled doors, wherein said pressing station is adapted toperform a pressing operation on at least a first of said assembled doorsin the first press while loading or discharging at least a second ofsaid assembled doors into or out of the second press, and wherein thefirst and second presses include a pressing surface shaped to compresscentral portions of the first and second door skins to a greater extentthan peripheral portions disposed about the perimeter of the first andsecond door skins, so that surfaces of the central portions and theperipheral portions of the first and second door skins are coplanar witheach other, and the peripheral portions are in contact with the stilesand rails of the door frame upon completion of the pressing operation;and at least one material handling device for transporting the assembleddoors between the stations.
 2. The door-making system of claim 1,wherein the at least one coating station comprises a first coatingstation for applying adhesive to the frame, a second coating station forapplying adhesive to the first door skin, and a third adhesive stationfor applying adhesive to the second door skin.
 3. The door-making systemof claim 2, wherein the first and second door skins comprise at leastone panel and the second and third coating stations apply a bead ofadhesive to the panels of the first and second door skins respectively.4. The door-making system of claim 1, wherein the door-making system isa synchronous system having a rate of movement and the pressing stationperforms a pressing operation on the at least two assembled doors for aperiod of time that is greater than the time to assemble a single door.5. The door-making system of claim 1, wherein the at least one assemblystation comprises a first assembly station for joining the first doorskin to the first surface of the door frame and a second assemblystation for joining the second door skin to the second surface of thedoor frame.
 6. The door-making system of claim 1, wherein the first andsecond presses each comprises an upper die having an upper convexsurface and a lower die having a lower convex surface.
 7. Thedoor-making system of claim 6, wherein the upper and lower convexsurfaces are integrally formed with the upper and lower dies,respectively.
 8. The door-making system of claim 6, wherein the upperand lower convex surfaces are removably connected to the upper and lowerdies, respectively.
 9. The door-making system of claim 6, wherein theupper and lower convex surfaces are constructed and arranged forimparting a concave shape to at least central regions of the first andsecond door skins of the door assembly during pressing.
 10. Thedoor-making system of claim 1, wherein the first and second presses eachcomprises an upper die having an upper membrane attached thereto and alower die having a lower membrane attached thereto, the upper and lowermembranes configured for compressing the central area of the first andsecond door skins to a greater extent than the peripheral portions ofthe first and second door skins.
 11. The door-making system of claim 1,further comprising a loading table upstream of said pressing station,said loading table adapted to load the assembled doors to both saidfirst and second presses.
 12. The door-making system of claim 11,wherein said loading table moves between first and second positionscorresponding to a location of said first and second presses.
 13. Thedoor-making system of claim 1, further comprising a discharging tabledownstream of said pressing station, said discharging table adapted tounload the assembled doors from both said first and second presses. 14.The door-making system of claim 13, wherein said discharging table movesbetween first and second positions corresponding to a location of saidfirst and second presses.
 15. A door pressing station, comprising: atleast first and second door presses vertically stacked relative to oneanother, the first and second door presses each comprising an upper diehaving an upper surface and a lower die having a lower surface, theupper and lower surfaces substantially spanning a width of said upperand lower dies, respectively, and facing one another to define a moldcavity in which a door assembly is received for pressing, each doorassembly comprising a door frame having stiles and rails forming aperimeter of the door frame, and a pair of door skins disposed onopposite sides of the door frame; a loading table upstream of said firstand second presses, said loading table adapted to load assembled doorsinto said first and second presses; and a discharging table downstreamof said first and second presses, said discharging table adapted tounload said assembled doors from said first and second presses aftereach door has been pressed, wherein the upper and lower surfaces of thedies of the first and second presses are shaped to compress centralportions of the pair of door skins to a greater extent than peripheralportions disposed about the perimeter of the pair of door skins, so thatsurfaces of the central portions and the peripheral portions of the pairof door skins are coplanar with each other, and the peripheral portionsare in contact with the stiles and rails of the door frame upondischarge.
 16. The door pressing station of claim 15, wherein the upperand lower surfaces are convex.
 17. The door pressing station of claim16, wherein the upper and lower convex surfaces are removably connectedto the upper and lower dies, respectively, or integrally formed with theupper and lower dies, respectively.
 18. The door pressing station ofclaim 16, wherein said upper and lower convex surfaces are continuouslycurving surfaces having a general parabolic shape with a vertexsubstantially at a center of said upper and lower dies, respectively.19. The door pressing station of claim 16, wherein said upper and lowerdies are formed with a flat section circumscribing said convex surfaces.20. The door pressing station of claim 19, wherein said flat section hasa width commensurate with a width of a stile of a door.
 21. A doorpressing station, comprising: at least first and second door pressesvertically stacked relative to one another, the first and second doorpresses each comprising an upper die having an upper compressiblesurface and a lower die having a lower compressible surface, the upperand lower compressible surfaces defining pressing regions of varyingshape facing one another to define a mold cavity in which a doorassembly is received for pressing; a loading table upstream of saidfirst and second presses, said loading table adapted to load assembleddoors to said first and second presses; and a discharging tabledownstream of said first and second presses, said discharging tableadapted to unload said assembled doors from said first and secondpresses, wherein the upper compressible surface of the upper diecomprises an upper convex surface, the lower compressible surface of thelower die comprises a lower convex surface, and wherein the upper andlower convex surfaces are configured to compress central portions of theassembled doors to a greater extent than peripheral portions disposedabout the perimeter of the assembled doors, so that surfaces of thecentral portions and the peripheral portions of the assembled doors arecoplanar with each other, and the peripheral portions are in contactwith stiles and rails forming a perimeter of a door upon discharge. 22.The door pressing station of claim 21, wherein the upper and lowerconvex surfaces are integrally formed with the upper and lower dies,respectively.
 23. The door pressing station of claim 21, wherein theupper and lower convex surfaces are removably connected to the upper andlower dies, respectively.
 24. The door pressing station of claim 21,wherein said upper and lower convex surfaces are continuously curvingsurfaces having a general parabolic shape with a vertex substantially ata center of said upper and lower dies, respectively.
 25. The doorpressing station of 21, wherein said upper and lower dies are formedwith a flat section circumscribing said convex surfaces.
 26. The doorpressing station of claim 25, wherein said flat section has a widthcommensurate with a width of a stile of a door.
 27. A door pressingstation, comprising: at least first and second door presses verticallystacked relative to one another, the first and second door presses eachcomprising an upper die having a first pressing surface and a lower diehaving a second pressing surface, the first and second pressing surfaceshave central regions that are closer to each other than peripheralregions to define a mold cavity in which a door assembly is received forpressing, wherein a compressible member is disposed along said upper andlower dies within said mold cavity; a loading table upstream of saidfirst and second presses, said loading table adapted to load assembleddoors to said first and second presses; and a discharging tabledownstream of said first and second presses, said discharging tableadapted to unload said assembled doors from said first and secondpresses, wherein the first and second pressing surfaces are shaped tocompress central portions of the assembled doors to a greater extentthan peripheral portions disposed about the perimeter of the assembleddoors, so that surfaces of the central portions and the peripheralportions of the assembled doors are coplanar with each other, and theperipheral portions are in contact with stiles and rails forming aperimeter of of a door upon discharge.
 28. The door pressing station ofclaim 27, wherein the first and second pressing surfaces are mounted tothe upper and lower dies, respectively.
 29. The door pressing station ofclaim 27, wherein the first and second pressing surfaces are removablyconnected to the upper and lower dies, respectively.
 30. A door-makingsystem, comprising: a pressing station comprising at least a first pressand a second press vertically stacked one on top of another, the firstand second presses each configured to receive, press, and discharge atleast one preassembled door having a door frame containing stiles andrails forming a perimeter of the door frame, at least two door skins,and adhesive, the first and second presses further being configured topress in alternating manner with respect to one another, wherein each ofthe first and second presses include dies shaped to compress centralportions of the at least two door skins to a greater extent thanperipheral portions disposed about the perimeter of the at least twodoor skins, so that surfaces of the central portions and the peripheralportions of the at least two door skins are coplanar with each other,and the peripheral portions are in contact with the stiles and rails ofthe door frame upon discharge.